2. STOCK-BASED COMPENSATION (Tables)

3 Months Ended

Aug. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Compensation costs related to the Company's stock-based compensation

The following table summarizes compensation costs related to the Company’s stock-based compensation for the three months ended August 31, 2015 and 2014 (in thousands):

	Three Months Ended
	August 31,
	2015		2014
Stock-based compensation in the form of employee stock options and ESPP shares, included in:
Cost of sales	$	22	$	14
Selling, general and administrative		238		148
Research and development		59		35
Total stock-based compensation	$	319	$	197

Assumptions for Options Valuation Model

The fair value of the Company’s stock options granted to employees for the three months ended August 31, 2014 were estimated using the following weighted average assumptions in the Black-Scholes option valuation model:

	August 31,
	2014
Option plan shares
Expected term (in years)		4
Volatility		0.91
Expected dividend	$	0.00
Risk-free interest rate		1.28	%
Estimated forfeiture rate		0.25	%
Weighted average grant date fair value	$	1.71

Stock option transactions

The following table summarizes the stock option transactions during the three months ended August 31, 2015 (in thousands, except per share data):

			Outstanding Options
							Weighted
				Number			Average		Aggregate
	Available			of			Exercise		Intrinsic
	Shares			Shares			Price		Value
Balances, May 31, 2015		845			3,686		$	1.66	$	2,946
Options granted		--			--			--
Options terminated		122			(122	)	$	2.04
Options exercised		--			(130	)	$	1.72
Balances, August 31, 2015		967			3,434		$	1.63	$	2,587
Options fully vested and expected to vest at August 31, 2015					3,366		$	1.63	$	2,535
Options exercisable at August 31, 2015					2,174		$	1.41	$	2,062

Options Outstanding

    The options outstanding and exercisable at August 31, 2015 were in the following exercise price ranges (in thousands, except per share data):

		Options Outstanding						Options Exercisable
		at August 31, 2015						at August 31, 2015
Range of Exercise Prices		Number Outstanding Shares		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price		Number Exercisable Shares		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price		Aggregate Intrinsic Value
$	0.59-$0.97		670		3.60	$	0.70		627		3.62	$	0.71
$	1.09-$1.40		1,257		3.75	$	1.28		921		3.47	$	1.28
$	1.73-$2.06		267		5.43	$	1.88		216		5.49	$	1.90
$	2.10-$2.71		1,240		6.12	$	2.45		410		5.85	$	2.53
$	0.59-$2.71		3,434		4.71	$	1.63		2,174		4.16	$	1.41	$2,062